1. Field of the Invention
The present invention relates to an image display device and a driving method thereof. More particularly, the present invention relates to an image display device and a driving method thereof in which image data is rewritable repeatedly.
2. Description of the Related Art
Conventionally, there has been proposed an image display method (which is simply referred to as ‘display method’ hereinafter) using a sheet-type image display medium on which image data is rewritable repeatedly, such as a twisting ball display (in which an image is displayed by turning particles each of which is painted by two colors), a medium using electric migration, a medium using magnetic migration, a thermal rewritable medium, or a storable liquid crystal medium. In such mediums, the thermal rewritable medium and the storable liquid crystal are excellent in storability. A display surface of each of the thermal rewritable medium and the storable liquid crystal cannot be so white as that of white paper. Therefore, when an image is displayed, a problem has been caused that it is difficult to visually recognize the difference between image portions and non-image portions on the surface, thus causing image quality to deteriorate.
On the other hand, the display method using the electric migration and the magnetic migration is such that the method has image storability and coloring particles are dispersed in white liquid. Such method is excellent in whitening the surface. However, because the white liquid always enters the gaps between coloring particles, a problem has arisen that black color for forming imaging portions of the surface becomes grayish, whereby image quality is deteriorated.
Because the white liquid is contained in the image display medium, when the image display medium is taken from the image display device roughly like when paper is handled, the white liquid may leak outside the image display device.
The twisting ball display is also excellent in image storability and has oil merely at cavities around particles inside the image display medium. The oil is almost in a solid state, and the image display medium is facilitated to form a sheet-type medium.
However, when white display is performed on the display surface of this medium by perfectly arranging white side semi-spherical surfaces of balls at a display side, and when light beams enter the gaps among the balls, the light cannot be reflected from the semi-spherical surfaces of the balls, whereby the light beams are lost inside the twisting ball display. Therefore, a problem has arisen in that 100% coverage of white cannot be displayed on the surface of the medium but slightly grayish white is displayed.
Further, the balls of twisting ball display are required to have a particle size that is smaller than a pixel size. Then, a problem is caused in that fine particles each of which is painted in two colors must be manufactured to display an image at high resolution, whereby a method in which the particles must be manufactured with high precision becomes necessary.
In order to solve the aforementioned problems, a display method using a toner has been proposed (toner display, Japan Hardcopy '99 reports (249–252 pp), Japan Hardcopy '99 fall reports (10–13 pp). The method is such that electrically conductive color toners and white particles are contained between electrode substrates facing each other. The electrically conductive color toners are charged through a charge transporting layer formed on the internal surface of the electrodes on a non-display substrate. The charged electrically conductive coloring toners are moved to a display substrate facing the non-display substrate, due to the electric field between the electrode substrates. The toners adhere at the internal portion of the display substrate to form an image due to a contrast between the toners and the white particles. This method is excellent in that the entire display medium is formed by solid matters and is able to perfectly switch over white-to-black or black-to-white.
Japanese Patent Application Laid-Open (JP-A) No. 2001-312225 discloses an image display medium that comprises a pair of substrates, and various types of particles each having different colors and different charging characteristics and included and movable between the pair of the substrates along the loaded electric field, and a driving method thereof in which a simple matrix driving is adopted, whereby an image can be displayed with high degree of whiteness and contrast.
However, by using this method, for example, when a line in a longitudinal direction of linear electrodes on a rear substrate is displayed on the image display medium by a simple matrix driving component, a problem has arisen in that pixels are caused to expand in the longitudinal direction of linear electrodes on the display substrate (i.e., a transverse direction of the linear electrodes on the rear substrate), and the width of the line becomes bold, thus making it difficult to display an image at high resolution.